| (Public
news item placed on the SORCE website)
SORCE
Observes Recent Dramatic Flare Activity –
By Gary Rottman
During the last week of October and the first
week of November the Sun surprised scientists with exceptionally
high levels of activity. The Sun has been carefully observed with
ever improving techniques since Galileo first pointed a telescope
at it in the early 1600s. The latest enhancements to our observational
capability are represented by the four new instruments on NASA’s
Solar Radiation and Climate Experiment, launched this past January.
It is indeed fortuitous that SORCE is available to record the
present “fireworks” on the Sun.
From historical observations we know that the
Sun moves through a cycle of activity approximately every eleven
years, changing from quiet to very active conditions and then
returning to its quiet state. The nature of this activity includes
the appearance of both bright regions, referred to as plage or
faculae, together with very dark sunspots. Both of these phenomena
are a manifestation of the Sun’s magnetic field erupting
from the interior and disturbing the bright surface layer of the
Sun. The Sun was very active in 2001 to 2002, and it was generally
felt that the Sun was well on its way back to its dormant state.
Scientists were therefore quite surprised recently when new and
intense magnetic activity appeared on the Sun. Indeed it is remarkable
that several of the largest sunspots ever recorded appeared and
moved across the solar disk during the week of October 26th.
When the Sun is active it is not unusual for
intense flares and coronal mass ejections to occur. These transient
phenomena carry large amounts of energy from the Sun to the Earth,
and often cause havoc within our environment. The energy comes
in two forms of radiation — light or electromagnetic energy
that travels at the speed of light and traverses the distance
from the Sun to the Earth in roughly eight minutes, and particles,
primarily electrons and protons that cover the distance in roughly
one day. When this transient energy reaches the Earth it interacts
in quite different ways. The particles are charged and must follow
the magnetic and electric fields of the Earth with a few penetrating
to lower levels of our atmosphere, and causing aurora, but only
in polar regions. These particles are so energetic that they easily
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GOES
Solar X-Ray Image, Nov 5, 2003. This large flare appeared just
beyond the limb.
pass through
spacecraft shielding and often damage sensitive electronics causing
satellite failures. In addition, the particles and fields energize
the very outer regions of our atmosphere and cause radio communication
interruptions. The intense electric fields generated by the particles
can also couple energy to power grids at the Earth’s surface
causing disruption and power outages.
The light
radiation from the flare is also very intense, but only in very
energetic X-rays (XPS) and far ultraviolet (SOLSTICE), and not
in the visible light that reaches the surface of the Earth (TIM).
This flare radiation is entirely absorbed in the upper layers
of our atmosphere where it also ionizes the atmosphere to interfere
with radio communication. Moreover, the intense radiation heats
the atmosphere and causes it to expand. The expansion increases
the atmospheric density at all altitudes, which in turn slows
satellites causing them to fall prematurely. The SORCE
instruments have done a spectacular job capturing these recent
flare incidents with great precision. These detailed measurements
will be extremely useful to the solar physics community. For the
TIM instrument, it is the first time that a TSI measuring instrument
has ever seen a flare. SOLSTICE observed factors of two to ten
increase in the ultraviolet while XPS recorded non-stop flare
activity over many days. The |
